Cell and Cell Structure Part-1

Cell and its Discovery

  • All living organisms are made up of microscopic unit known as cells.
  • Cell is the basic structural and fundamental unit of all living organisms.
  • Cell was first discovered and observed by Robert Brown in 1665 in a cork slice with the help of a primitive microscope.
  • In 1674, Leeuwenhoek discovered first free living cell.
  • Robert Brown (1831) discovered nucleus in the cell.

Cell theory

  • In 1838, two biologists Schleiden and Schwann proposed a cell theory and states that all plants and animals are composed of cells and cell is the basic unit of life.
  • Virchow further expands the cell theory and suggests that all cells arise from pre-existing cells.

Types of organisms

  • Unicellular Organisms- Single celled organisms that performs the all the functions of the body. Example- Paramecium, Amoeba, Bacteria.
  • Multicellular Organism – Composed of many cells and grouped together to perform different function of the body. Example- Plants, fungi and Animals.

Types of Cells

There are presences of two types of cells- Prokaryotic and Eukaryotic cells.

  • Prokaryotic cell- These cells are simple and lack a well-defined nucleus.
  • Eukaryotic cell- These cells are more developed with a well defined nucleus.
  • Ostrich egg is the largest cell in world while in human being largest cell is nerve cells.

 

 

Difference between Prokaryotic and Eukaryotic cells

Prokaryotic cells

Eukaryotic cells

The nucleus and nucleolus are not found

The nucleus and nucleolus are present

Membrane-bound organelles are absent

Membrane-bound organelles can be seen

Reproduction is asexual

Reproduction is both sexual and asexual

Always unicellular

Often multicellular

Contain a single chromosome

Contain multiple chromosomes

Budding or fission cell division

Mitotic or meiotic cell division

Example-Bacteria, Blue Green Algae etc.

Example-Fungi ,Plant Cell, Animal Cell

 

Difference between Plant and Animal cells

Plant Cells

Animal Cells

A rigid cell wall encapsulates the plasma membrane

No cell wall present

Larger than animal cells

Much smaller than plant cells

Contain plastids

Do not contain plastids (except protozoan Euglena)

Vacuoles are large and permanent

Vacuoles are small and temporary

Do not contain centrosomes and centrioles

Do contain centrosomes and centrioles